Automatic volume control circuit



Sept. 6, 1938. E ZEPLER 2,129,078

AUTOMATIC VOLUME CONTROL CIRCUIT Filed Sept. 2, 193a MIAAVAVAVMA [7C HIV! INVENTOR ERICH ZEPLER ATTO RN EY Patented Sept. 6, 1938 PATENT OFFICE AUTOMATIC VOLUME CONTROL CIRCUIT Erich Zepler, Chelmsford, England, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Application September 2, 1936, Serial No. 99,032 In Germany September 17, 1935 4 Claims.

The present invention relates to an arrangement adapted to compensate for attenuation of high modulation frequencies caused by unduly narrow or peaked resonance curves.

It is known from actua1 practice in radio reception that there occurs often an undue cut-off of the side-bands, and thus a weakening of the high pitched notes, because of the abrupt drop, or the steepness, of the flanks or sides of resonance curves. To be sure, this undesired cut-off may be avoided to a certain extent by the aid of band-pass filters, though a great number thereof must be provided in order that adequate steepness of the flanks of the resonance curves. may be obtained to thus prevent undue impairment in selectance. Another way and means to establish balanced and uniform conditions consists in that, in the audio network, the lowpitched notes are slighted in comparison to the high audio frequencies. However, this is of great disadvantage insofar as in the case of disk reproduction of sound, uniform amplification or even a preferential treatment of the low audio frequencies is desirable.

For these reasons another procedure is disclosed in this application whereby the said drawbacks are obviated. The present invention consists in that the time-constant of automatic fading compensation, or volume control, is chosen so low that the amplification, for low modulation frequencies, is less than for the high frequencies.

In the drawing is illustrated an exemplified embodiment adapted to practicing the present invention. From the aerial the radio frequency potential is fed by way of the radio amplifier HF and coupling means (not shown), or additional stages, to the rectifier G which, in this instance, furnishes at the same time the regulator, or biasing, voltage. In the exemplified embodiment here illustrated two filter units, or meshes, are provided through which the regulating voltage is applied. The resistances W1 and W2 as well as the condensers C, C1 and C2 must be chosen sufficiently low, but not too low to prevent the high notes. being compensated away. The low frequencies are attenuated by that, upon an increase of the radio frequency amplitudes, the gain or amplification is reduced, while upon a rise (at the frequency of the low notes) the gain is raised with the result that at the output end of the radio frequency amplifier the high frequency oscillations will be less modulated by the low notes.

If because of the reduction in value of the resistances W1 and W2 the filter effect for the highfrequency waves should prove to be insuflicient, it would be possible, for instance, to insert an RF choke in lieu of a resistance. The letters NF denote the audio frequency path for utilizing the audio voltage developed across diode load resistor W3.

What is claimed is:

1. In a radio receiver of the type comprising a signal transmission tube and a single rectifier in cascade, said transmission tube having signal carrier selector resonant networks associated therewith which are sufiiciently sharp to produce attenuation of the higher modulation signal frequencies, means in circuit with the rectifier producing a direct current voltage whose value varies directly with the carrier amplitude, only a single network for applying said Voltage to the transmission tube in a sense to reduce the gain thereof, and the time constant of said last network being chosen sufficiently low so that the 20 gain of the transmission tube is less for low modulation frequencies than for the aforesaid higher modulation frequencies whereby the said attenuation is compensated for.

2. In a radio receiver of the type comprising a signal transmission tube and a single rectifier in cascade, said transmission tube having signal carrier selector resonant networks associated therewith which are sufiiciently sharp to produce attenuation of the higher modulation signal 30 frequencies, means in circuit with the rectifier producing a direct current voltage whose value varies directly with the carrier amplitude, only a single network of at least two filter meshes for applying said voltage to the transmission tube 35 in a sense to reduce the gain thereof, and the time constant of said last network being chosen sufiiciently low so that the gain of the transmission tube is less for low modulation frequencies than for the aforesaid higher modulation frequencies whereby the said attenuation is compensated for.

3. In a radio receiver of the type comprising a signal transmission tube and a single rectifier in cascade, said transmission tube having signal carrier selector resonant networks associated therewith which are sufficiently sharp to produce attenuation of the higher modulation signal frequencies, means in circuit with the rectifier producing a direct current voltage whose value varies directly with the carrier amplitude, only a single network for applying said voltage to the transmission tube in a sense to reduce the gain thereof, and the time constant of said last network being chosen sufiiciently low so that the gain of the transmission tube is less for low modulation frequencies than for the aforesaid higher modulation frequencies whereby the said attenuation is compensated for, said rectifier acting as the demodulator of the receiver, said rectifier being of the diode type.

4. In a receiver of side band modulated carrier signals, an amplifier for the signals, signal selector networks sufficiently sharp to cause side 10 band cutting, solely a single automatic gain con- 

